This invention relates to optical fiber connectors, and, more particularly, to an optical fiber connector for use with robust optical fiber.
In optical fiber communications, connectors for joining fiber segments at their ends, or for connecting optical fiber cables to active or passive devices, are an essential component of virtually any optical fiber system. The connector or connectors, in joining fiber ends, for example, has, as its primary function, the maintenance of the ends in a butting relationship such that the core of one of the fibers is axially aligned with the core of the other fiber so as to maximize light transmissions from one fiber to the other. Another goal is to minimize back reflections. Such alignment is extremely difficult to achieve, which is understandable when it is recognized that the mode field diameter of, for example, a singlemode fiber is approximately nine (9) microns (0.009 xcexcm.) Good connection (low insertion loss) of the fiber ends is a function of the alignment, the width of the gap (if any) between the fiber ends, and the surface condition of the fiber ends, all of which, in turn, are inherent in the particular connector design. The connector must also provide stability and junction protection and thus it should minimize thermal and mechanical movement effects.
In the present day state of the art, there are numerous, different, connector designs in use for achieving low insertion loss and stability. In most of these designs, a pair of ferrules (one in each connector), each containing an optical fiber end, are butted together end to end within a connector adapter and light travels across the junction. Zero insertion loss requires that the fibers in the ferrules be exactly aligned, a condition that, given the necessity of manufacturing tolerances and cost considerations, is virtually impossible to achieve, except by fortuitous accident. As a consequence, most connectors are designed to achieve a useful, preferably predictable, degree of alignment, some misalignment being acceptable.
Alignment variations between a pair of connectors are most often the result of the offset of the fiber core centerline from the ferrule centerline. This offset, which generally varies from connector to connector, is known as xe2x80x9ceccentricityxe2x80x9d, and is defined as the distance between the longitudinal centroidal axis of the ferrule at the end face thereof and the centroidal axis of the optical fiber core held within the ferrule passage.
There are numerous arrangements in the prior art for xe2x80x9ctuningxe2x80x9d a connector, generally by rotation of its ferrule, to achieve an optimum direction of its eccentricity. One such arrangement is shown in U.S. Pat. No. 5,481,634 of Anderson et al, wherein the ferrule is held within a base member which may be rotated to any of four rotational or eccentricity angular positions. In U.S. Pat. No. 4,738,507 of Palmquist there is shown a different arrangement and method for positioning two connectors relative to each other for minimum insertion loss or maximum coupling. In U.S. Pat. No. 6,155,146 of Andrews, et al. there is shown still another arrangement for tuning a coupler, in which the ferrule, which is mounted in a barrel having a front flange member having six positions of rotation, can be rotated to that one of the six positions producing the most favorable result. In U.S. Pat. No. 6,663,293 of Lampert and Lewis, issued Dec. 16, 2003, another tunable optical fiber connector is shown.
In virtually all such connectors, stability arid resistance to various types of mechanical stress, such as, for example, an accidental xe2x80x9cpullxe2x80x9d stress on the cable, or other stresses which, conceivably can disrupt the tuning, are highly desirable, if not essential to proper operation of the connector. This is especially true of jumper cables with connectors at each end. A large measure of the xe2x80x9cpull-proofxe2x80x9d characteristic is present where the optical fiber has strength members, such as aramid yarn, incorporated into a coating or jacket surrounding the fiber or cable. These strength members are generally firmly attached, as by crimping, to the connector and any pull stresses are applied to the aramid fibers and not to the optical fiber which is, therefore, efficiently shielded from the stresses. However, strength members and materials represent an added expense to the cost of the connector.
A recent advance in the optical fiber art has been the development of what is commonly referred to as xe2x80x9crobustxe2x80x9d optical fiber, which has a core that is substantially the same size or diameter as that of more conventional fibers, but has a core cladding that is materially greater in diameter (or thickness) than the cladding of prior art fibers. Robust fiber has a core plus cladding diameter of approximately two hundred microns (200 xcexcm) whereas conventional fiber has a diameter of one hundred twenty-five microns (125 xcexcm). Robust fiber has many advantages over conventional fiber, as pointed out in the aforementioned related DiGiovanni et al application, among which is a sufficient fiber strength to resist many of the stresses encountered in use. As such, the robust fiber doesn""t require the aramid strength members in general usage. However, there then is no separate strength member such as the aramid fiber to absorb high axial loads, and these loads, as well as other stresses are applied directly to the fiber. Further, with enough axial tension stress the ferrule of the connector can be pulled out of engagement with the ferrule of the other element in the connection, such as another connector, thereby disrupting low loss communication between the two, or, in extreme cases, resulting in complete disconnection.
The present invention, shown hereinafter as incorporated in a modified LC connector for optical fiber, more particularly for robust fiber, assures that the connector is substantially pull proof. While an LC connector is shown hereinafter in a preferred embodiment of the invention, it is to be understood that the principles and features of the invention are applicable to other types of connectors as modified.
The basic structure of an LC type connector includes a ferrule-barrel assembly for holding the end of an optical fiber which extends axially therethrough and a housing which holds the ferrule-barrel assembly. The housing has a latching arm for latching the connector in a mating connector adapter, for example. A coil spring member contained within the housing surrounds the barrel and bears against, for example, an interior wall of the housing and a flange portion of the barrel, thereby supplying forward bias to the ferrule-barrel assembly relative to the housing. The flange portion generally is shaped to be supported within an interior cavity or seat of the housing in any one of, for example, six rotational orientations with respect to the central axis of the fiber holding structures. A ferrule extends axially from the barrel member and contains a fiber end therein. The connector is thus tunable to any one of six possible rotational orientations by axially pulling the flange portion away from the seat sufficient to free it for rotation.
In a first illustrative embodiment of the invention, the fiber contained in the ferrule is a robust fiber having a diameter of at least 200 xcexcm. The barrel includes a tubular portion extending rearwardly of the flange portion, with the ID thereof enlarged to accommodate the enlarged coated and jacketed fiber. In normal use the ferrule moves rearwardly from the polished end face to reach the optical plane (OP), a distance of approximately 0.020 inches, for example. However, the ferrule assembly can move rearwardly a much greater distance in a normal LC connector, and the opposing ferrule can follow up to approximately 0.020 inches to prevent decoupling. In a normal pull-proof connector the aramid yarns take up the tensile load. A cable retention tubular member which functions as a stop member is axially aligned with the barrel and fixedly mounted within the housing. The inner diameter (ID) of the retention member is less than the outer diameter (OD) of the tubular portion of the barrel so that when the barrel member is axially moved toward the rear of the connector, a distance of, for example, 0.025 inches the end of the tubular portion butts against the end of the retention member and is prevented from moving further. Thus, the connector of the invention is pull-proof, allowing a limited rearward axial movement of the barrel, and, hence, the ferrule without optical disconnect. The distance the ferrule is allowed to move is limited to the distance over which the spring loaded connecting ferrule or other device will follow the ferrule, retaining contact therewith. It should be noted that a tunable barrel as shown in the aforementioned Lampert and Lewis application can also be used for optical tuning, or it can be pre-tuned.
In a second embodiment of the invention the housing has a substantially rectangular or square window or opening in each of the side walls thereof, and a U-shaped retainer member in inserted therein and embraces a portion of the barrel, with one end butting against a shoulder of the flange on the barrel. The retainer member is axially movable within the opening until it butts against the rear edge of the opening, thus preventing further rearward movement of the barrel. The rear edge of the opening and the width of the U-shaped member are chosen to permit an axially rearward movement of the ferrule containing barrel flange of from 0.020 to 0.035 inches without disconnect.
An advantage of the arrangement of the second embodiment is that the retainer member may be removed to allow sufficient rearward movement of the barrel sufficient to free the barrel from its hexagonal seat in the housing for tuning by rotation thereof. After tuning, the retainer member may again be inserted into the window to embrace the barrel.
In both embodiments of the invention, the latching arm has one or two latching side protruding latches which are adapted to engage latching shoulders within the adapter when the connector is inserted therein and latched. In order to insert and withdraw the connector, the latching arm (and connector) is moved forward and depressed until the latches are out of engagement with the latching shoulder. Inasmuch as the latching arm is pivoted, the latches are swung in an arc when the arm is depressed, and there must be sufficient clearance space for the latches to be disengaged. This necessary clearance space encroaches on the backward travel space of the barrel/ferrule assembly, thus, limiting undesirably the amount of backward travel available. In the present invention, the latches are back cut so that only a narrow bottom strip portion thereof is adapted to bear against the latching shoulders, and as a result, the amount of clearance necessary is reduced, thereby permitting more backward travel of the ferrule/barrel assembly.
The principles and features of the present invention as set forth briefly hereinbefore, will be more readily apparent from the following detailed description, read in conjunction with the drawings.